In late 2010, Ishii started a storyline rivalry with masked wrestler Tiger Mask, going after his mask on several occasions. This built to a match during the first Fantasticamania weekend on January 23, 2011, where Tiger Mask defeated Ishii in a Lucha de Apuestas Mask vs. Hair match; as a result, Ishii was forced to have his head shaved. After the shaving, Ishii once again attacked his rival and unmasked him. During the next NJPW event three days later, Ishii continued his rivalry with Tiger Mask, but was now wearing the mask of Black Tiger, a longtime nemesis of the various Tiger Masks that have appeared in NJPW throughout the years. The rivalry culminated on February 20 at The New Beginning, where Tiger Mask defeated Ishii in a Mask vs. Mask match, taking away his mask and ending the rivalry. Though Ishii worked the entire rivalry under his real name, he was officially recognized by NJPW as the sixth generation Black Tiger, when Kazushige Nosawa debuted in 2012, billed as the seventh generation Black Tiger. In June 2011, Ishii took part in the J Sports Crown Openweight 6 Man Tag Tournament, where he and Chaos stablemates Takashi Iizuka and Toru Yano made it to the semifinals, before losing to Giant Bernard, Jushin Liger and Karl Anderson.

After having worked for NJPW for eight years, Ishii received his first title shot in the promotion on May 20, 2012, when he unsuccessfully challenged Hirooki Goto for the IWGP Intercontinental Championship in the main event of a show in Osaka. The following November, Ishii took part in a tournament to determine the inaugural NEVER Openweight Champion. After wins over Daisuke Sasaki and Yoshi-Hashi, Ishii was defeated in the semifinals of the tournament by Chaos stablemate Masato Tanaka, who went on to win the entire tournament. The following month, Ishii teamed with Chaos leader Shinsuke Nakamura in the 2012 World Tag League, where they picked up three wins out of their six matches, failing to advance from their round-robin block. In January 2013, Ishii took part in the third Fantasticamania weekend, winning a twelve-man torneo cibernetico on January 20. Following the win, Ishii challenged Masato Tanaka to a rematch for the NEVER Openweight Championship. The rematch between the two stablemates took place on February 3 in a main event at Korakuen Hall. Despite having the audience noticeably behind him, Ishii was again defeated by Tanaka, who, as a result, retained his title. The match was later praised by sports journalist Dave Meltzer, though he also expressed concern for the healths of both Ishii and Tanaka following the hard-hitting match. For his fan following, Ishii earned himself the nickname "New Mr. Korakuen". On March 11, Ishii picked up his biggest singles win in his NJPW career, when he defeated multi-time IWGP Heavyweight and IWGP Tag Team ChampionSatoshi Kojima in the first round of the 2013 New Japan Cup. Six days later, Ishii was defeated in his second round match in the tournament by Hirooki Goto. In early 2013, Ishii also became involved in Chaos' rivalry with Suzukigun, NJPW's other major villainous stable, leading to Chaos and Ishii being positioned in a more sympathetic role than usual. On March 23, Ishii teamed with Jado and Shinsuke Nakamura to defeat Suzukigun representatives Minoru Suzuki, Lance Archer and Taka Michinoku in a six-man tag team match by pinning Michinoku for the win. After the match, Nakamura challenged Archer and his tag team partner Davey Boy Smith, Jr. to a match for the IWGP Tag Team Championship, nominating Ishii as his partner for the match. Ishii and Nakamura received their title shot on April 5, but were defeated by Archer and Smith. Ishii then got involved in a heated rivalry with Suzukigun leader Minoru Suzuki, which built to a singles match between the two on July 20 at the Kizuna Road 2013pay-per-view, where Suzuki was victorious. As a sign of his rising status in NJPW, on August 1, Ishii entered the 2013 G1 Climax, his first ever entry into the promotion's premier tournament. Ishii main evented the second night of the tournament in Korakuen Hall, where he picked up a major win over six-time IWGP Heavyweight Champion Hiroshi Tanahashi. On the fourth night of the tournament, Ishii defeated Katsuyori Shibata in a match that received widespread acclaim, including a five-star rating from Dave Meltzer. Ishii's only other win in the tournament came via forfeit over the injured Hirooki Goto, a result that left him at the bottom of block A. Following the tournament, NJPW announced that Ishii would embark on his first tour with Mexican promotion Consejo Mundial de Lucha Libre (CMLL) starting September 8. Ishii made his CMLL debut on September 13 at the 80th Anniversary Show in Mexico City, teaming with compatriots Namajague and Okumura to defeat Fuego, Rey Cometa and Stuka, Jr. in a six-man tag team match. Ishii remained in CMLL until October 1, working undercard six-man tag team matches. Ishii wrestled his NJPW return match on October 14 at King of Pro-Wrestling, when he was defeated by Katsuyori Shibata in a rematch of their highly acclaimed G1 Climax match. From November 23 to December 7, Ishii and Shinsuke Nakamura took part in the 2013 World Tag League, where they finished with a record of three wins and three losses, with a loss against Togi Makabe and Tomoaki Honma on the final day costing them a spot in the semifinals.

On January 5, 2014, Ishii started a new storyline rivalry with Tetsuya Naito, announcing his intention of becoming the next NEVER Openweight Champion. The title match between the two took place on February 11 at The New Beginning in Osaka and saw Ishii become the third NEVER Openweight Champion, winning his first title in NJPW. After Naito eliminated Ishii from the 2014 New Japan Cup in their first round match, a rematch for the NEVER Openweight Championship between the two was set for the April 6 Invasion Attack 2014 event, where Ishii made his first successful title defense. Ishii's second successful title defense took place just six days later during NJPW's trip to Taiwan, when he defeated Kushida. On May 3 at Wrestling Dontaku 2014, Ishii made his third successful title defense against Tomoaki Honma and was afterwards challenged by IWGP Junior Heavyweight ChampionKota Ibushi, with whom he had had sporadic heated encounters since the past year's G1 Climax. The match between the two took place on May 25 at Back to the Yokohama Arena and saw Ishii make his fourth successful title defense. After the match, Ishii was pulled into the rivalry between Chaos and Bullet Club, when he was attacked by former stablemate Yujiro Takahashi, who appointed himself as his next challenger.